Re: [Cfrg] A little room for AES-192 in TLS?

"Paterson, Kenny" <> Mon, 16 January 2017 17:37 UTC

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From: "Paterson, Kenny" <>
To: Eric Rescorla <>, John Mattsson <>
Thread-Topic: [Cfrg] A little room for AES-192 in TLS?
Date: Mon, 16 Jan 2017 17:37:25 +0000
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Cc: "" <>, Leonard den Ottolander <>
Subject: Re: [Cfrg] A little room for AES-192 in TLS?
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On 16/01/2017 16:27, "Cfrg on behalf of Eric Rescorla"
< on behalf of> wrote:

>Generally, I think the sense of the WG is to try to minimize the number
>of ciphers/suits.
>Speaking personally, what would make me be in favor of adding AES-192
>would be
>some statement from CFRG that they thought that it was significantly
>stronger than
>AES-256. Absent that, I think it would be better to leave it out of TLS.

Speaking without my co-chair's hat on...

I don't think related-key attacks are a particular concern for TLS. So I
don't think there's a strong argument for supporting AES-192 in the TLS
1.3 protocol specification.

Anyone else from CFRG have an opinion on this?



>On Mon, Jan 16, 2017 at 7:59 AM, John Mattsson
><> wrote:
>Note that there are trivial generic related-key attacks on AES-192 with #K
>= D = T = M = 2^96
>On 2017-01-16, 15:43, "Cfrg on behalf of Leonard den Ottolander"
>< on behalf of
>> wrote:
>>On Sun, 2017-01-15 at 20:59 +0000, Taylor R Campbell wrote:
>>> Only very unusual protocols ever use related keys.  In sensible
>>> protocols, every key is drawn independently uniformly at random.
>>Protocols that are designed to use related keys? I hope not!
> <> 4.1
>Related-key attack model:
>>"Compared to other cryptanalytic attacks in which the attacker can
>>late only the plaintexts and/or the ciphertexts the choice of the
>>relation between
>>secret keys gives additional degree of freedom to the attacker. The
>>downside of
>>this freedom is that such attacks might be harder to mount in practice.
>>designers usually try to build "ideal" primitives which can be
>>automatically used
>>without further analysis in the widest possible set of applications,
>>protocols, or
>>modes of operation. Thus resistance to such attacks is an important
>>design goal
>>for block ciphers, and in fact it was one of the stated design goals of
>>the Rijndael
>>algorithm, which was selected as the Advanced Encryption Standard."
>>So the question remains if indeed AES-192 is inherently more resistant
>>to this kind of attack (more of an "ideal primitive" in this respect)
>>than AES-256 or do I read too much in the remark "the key schedule of
>>AES-192 has better diffusion" in 6 Attack on AES-192?
>>mount -t life -o ro /dev/dna /genetic/research
>>Cfrg mailing list
>Cfrg mailing list